Electrically conductive materials are used for a variety of purposes in the fabrication and assembly of electronic devices, integrated circuits, semiconductor devices, and solar cells and/or solar modules. For example, electrically conductive adhesives are used to bond integrated circuit chips to substrates (die attach adhesives) or metal tabs to the surfaces of solar cells.
For a broad variety of different applications electrically conductive materials, such as electrically conductive adhesives (ECAs), can be regarded as a promising alternative to solder materials as interconnect materials. In general, ECAs provide a mechanical bond between two surfaces and conduct electricity. Typically, ECA formulations are made of a polymer resin filled with electrically conductive metal fillers. The resin generally provides a mechanical bond between two substrates, while the electrically conductive fillers generally provide the desired electrical interconnection. Typically, ECAs offer the following advantages: lower processing temperatures, reduced environmental impact, and increased resistance to thermomechanical fatigue.
For instance, U.S. Pat. No. 6,344,157 B1 discloses an electrically conductive adhesive with improved electrical stability for use in microelectronic applications, which comprises a polymeric resin, a conductive filler, a corrosion inhibitor, and a low melting point metal filler, wherein the low melting point metal filler can be selected from indium, indium alloys, tin alloys or mixtures thereof. The polymeric resin can be selected from the group consisting of vinyl-, acrylic-, phenol-, epoxy-, maleimide-, polyimide-, or silicon-containing resins. The above referenced U.S. patent does not disclose the combination of cyanate esters and epoxy resins as the polymeric resin component.
While conductive adhesives having conductive fillers may have potential advantages in electrical conduction applications, they may also pose challenges, such as the relatively low electrical conductivity of the polymeric portion of the adhesive. Moreover, a particular challenge with metal-filled adhesives is implementing the appropriate balance of filler loading, adhesive strength, curing speed, electrical conductivity and stable electrical contact resistance.
Hence there is a need for new adhesives having electrically conducting properties in order to achieve the desired adhesion, curing speed, electrical conductivity and stable electrical contact resistance.